Formula for Buoyancy

Archimedes principle works for any fluid, but as divers we are mainly concerned with two different fluids: fresh water, and salt water. We need to think of fresh water and salt water as two different fluids because equal volumes of fresh water and salt water do not weigh the same.Archimedes’ principle does not consider the surface tension(capillarity) acting on the body.

Archimedes realized that an object immersed in fluid will be lighter by an amount equalto the weight of the fluid it displaces. This upward force exerted on the object by thefluid is known as the buoyant force:

FB = g ρF V

where:FB is the buoyant force on the object,g is the acceleration due to gravity,ρF is the density of the fluid, andV is the volume of the object immersed in a fluid.